Metallurgical coke is used to make steel. Production facilities for making coke include both non-recovery coke ovens and byproduct coke ovens as the two major types of coke ovens. There exists a great need for an alternative use of coke ovens during downturns in the highly cyclical steel industry. Currently in North America approximately 55% of the crude steel produced is via an electric arc furnace (EAF) route, and 45% is produced via the blast furnace (BF) route. During downturns in steel demand the EAF operators can simply turn off the furnaces and wait for demand to recover. The EAF's produce crude steel by melting scrap metal and refining the molten metal in downstream ladle furnace. Historically the EAF's major markets have been construction materials such as reinforcing bars, and steel columns and beams. Sheet steel is also supplied to the “white goods” manufacturers, such as washers, dryers and refrigerators. A smaller percentage of the market for EAF operators is the higher value sheet steel (coils) for auto and truck bodies.
Blast furnace operators who produce crude steel utilizing iron ore and coke have a much more difficult time in throttling production during periods of low steel demand. This is because BF's are very large (i.e., BF's use 7.6 to 15 meters in diameter by 30.5 meters or more tall) ultra-high temperature counter current production reactor vessels which cannot be easily stopped or re-started. A typical BF campaign (continuous production) typically lasts 5-15 years. BF's can decrease crude steel production by slowing down the BF's and in the extreme case shutting them down completely until steel demand recovers.
Approximately 30% of the coke produced in North America is produced in what are called non-recovery, or heat recovery or horizontal ovens, while the remaining 70% is produced in what are called by-product or slot or vertical coke ovens. Unlike EAF's or BF's, once heated up coke ovens cannot be shut down or allowed to go cold.
Another ongoing need in the steel industry is the disposal of a typical steel mill waste known as mill scale. Mill scale is produced within the rolling mill operations of a steel mill and is a mixture of iron and iron oxides that is typically contaminated with oils and lubricants used in the rolling process. Typically steel billets or slabs are reheated to about 1100° C. (2012° F.) in a reheat furnace. The hot steel is then processed in the rolling mill and shaped into the desired end product mix such as rebar, angles, I-beams and sheet steel. Given that the steel is heated to a high temperature and is exposed to oxidizing agents such as air and water in the rolling mill, the surface of the steel is oxidized and forms flakes (also known as scale) which is flaked off during the rolling operations. It is known that from 1-5 weight % of the crude steel produced actually winds up as mill scale. More typically the range is 2-3 weight %. Given that North American steel production is typically about 82 million metric tons per year, this equates to an annual mill scale generation rate of 1.6 to 2.4 million metric tons per year.
In view of the foregoing embodiments of the disclosure provide a high value steel/carbon product from a low value iron-containing waste material and process for producing the steel/carbon product. The high value steel/carbon product is derived from a mixture of metallurgical coal and an oxidized iron waste material under a reducing atmosphere. The steel/carbon product has a porosity of greater than about 60% and a density of greater than about 900 kg/m3 and the steel component of the steel/carbon product has a percentage of metalization of greater than about 85 wt. %. By contrast, metallurgical coke has a porosity of about 50% or less.
In another embodiment, the disclosure provides a process for the simultaneous production of coke and a steel/carbon product. The process includes mixing metallurgical coal with an oxidized iron waste material in a weight ratio of from greater than 1:1 to about 5:1 to provide a coal/oxidized iron mixture. The coal/oxidized iron mixture is size reduced so that from about 80 to about 95 wt. % is less than about 5 millimeters. The reduced size mixture is fed to a coke oven. The mixture is heated in the coke oven to a temperature of less than about 1250° C. for a period of time sufficient to convert the coal to coke and to reduce iron oxides in the oxidized iron waste material to iron, whereby the coke and iron form a steel/carbon product. The steel/carbon product is then quenched.
An advantage of the embodiments of the disclosure is that it provides a high value raw material source for making iron from a waste material that has little value. Another important advantage of the embodiments of the disclosure is that production of the steel/carbon product enables certain coke ovens to continue to operate even during a downturn in demand for steel by producing an alternative product in otherwise idle coke ovens.